1. Field of the Invention
The present invention relates in general to a method for manufacturing ink jet printheads and the product printheads derived therefrom, and, more particularly, to a method for electro-deposition passivation of ink channels in ink jet printheads and printheads with ink channels passivated by such method.
2. Description of the Related Art
Printers provide a means of outputting a permanent record in human readable form. A printing technique may generally be categorized as either impact printing or non-impact printing. A popular form of non-impact printing is referred to as ink jet printing. In ink jet printing, ink is ejected, most commonly by pressure, through a tiny nozzle to form an ink droplet that is deposited upon a paper medium. Such ink jet printing devices produce highly reproducible and controllable droplets, so that a droplet may be printed at a location specified by digitally stored data.
Most commercially available ink jet printing systems may be generally classified as either "continuous jet" or "drop-on-demand" ink jet printing systems. In a continuous jet ink jet printing system, ink droplets are continuously ejected from the printhead and either directed to or away from the paper or other substrate depending on the desired image to be produced. In a drop-on-demand ink jet printing system, ink droplets are ejected from the printhead in response to a specific command related to the image to be produced.
Drop-on-demand ink jet printing systems are based upon the production of droplets by electromechanically induced pressure waves. The ink is typically stored in a reservoir or channel. A volumetric change in the ink fluid so stored is then induced by the application of a voltage pulse to an electromechanical material, such as a piezoelectric material, which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid and these are directed so as to produce a droplet that issues from the reservoir or channel, typically through an orifice. Since the voltage is applied only when a droplet is desired, these types of ink jet printing systems are referred to as drop-on-demand.
The use of piezoelectric materials in ink jet printers is well known. Most commonly, piezoelectric materials are used in a piezoelectric transducer by which electric energy is converted into mechanical energy by applying an electric field across the material, thereby causing the piezoelectric material to deform. This ability to deform piezoelectric material has often been utilized in order to force the ejection of ink from the ink reservoirs, passages or channels of drop-on-demand type systems. Illustrative patents showing the use of piezoelectric materials in ink jet printers include U.S. Pat. Nos. 3,857,049, 4,584,590, 4,825,227, 4,536,097, 4,879,568, 4,887,100, 5,227,813, 5,235,352, 5,334,415, 5,345,256, 5,365,645, 5,373,314, 5,400,064, 5,402,162, 5,406,319, 5,414,916, 5,426,455, 5,430,470, 5,433,809, 5,435,060, 5,436,648 and 5,444,467.
One drop-on-demand type ink jet printer configuration which utilizes the distortion of a piezoelectric material to eject ink includes a printhead forming an ink channel array in which the individual channels of the array each have side walls formed at least, in part, of a piezoelectric material. In the typical case of such an array, the channels are microsized and are arranged such that the spacing between adjacent channels is relatively small. In operation of this type printhead, ink is directed to and resides in the channels until selectively ejected therefrom. Ejection of ink from selected channels is effected due to the electromechanical nature of the piezoelectric side walls of the channels. Because piezoelectric material deforms when an electric field is applied thereacross, the side walls of selective channels may be caused to deform by applying an electric field across select ones thereof. The electric field may be so selectively applied by digital or other means. This deformation of side walls of select channels reduces the volume of the respective channels creating a pressure pulse in the ink residing in those channels. The resultant pressure pulse then causes the ejection of a droplet of ink from the front end of the particular channel adjacent the side walls across which the electric field is applied.
Many ink jet printheads also include a cover plate fixedly mounted on the front end of the printhead adjacent the ink channels. Extending through such a cover plate may be a plurality of orifices which comprise an array. In most ink jet printheads, each orifice in such an orifice array corresponds to one of the ink channels of the printhead. A cover plate is typically positioned abutting the printhead in a manner so that each orifice is in communication with a corresponding channel of the printhead. When a pressure wave is created in ink in a typical ink jet printhead due to electromechanical action or otherwise, an ink droplet is forcibly ejected from the ink jet printhead through the orifice. This type of orifice can form an appropriate ink droplet to create a desired impression as the droplet is thereby deposited on a selected medium.
In a typical configuration, the electrical conductors used to apply the electric field across the piezoelectric material of the channels extend to the edge of and are exposed within the walls of the channels. Accordingly, when conductive fluids, such as water-based inks are disposed within the channels of such ink jet printheads (such as described in U.S. Pat. Nos. 4,879,568, 4,887,100, 5,227,813 and 5,235,352, which are incorporated herein by reference), electrical current flows through the fluid and degradation in performance will occur unless there is complete protection or isolation of the active piezoelectric material or electrical conductors on the piezoelectric material from the conductive fluids. Degradation can consist of bubble formation upon the application of an electric field to actuate the ink carrying channels resulting in printing errors. Degradation can also consist of shorting of the electric field in the piezoelectric material which is in contact with the conductive fluid. Degradation can further consist of chemical attack of the active piezoelectric material by the conductive fluid. The current flow and degradation in performance results in printing errors. There is a need, therefore, for an ink jet printhead in which the electrical conductors disposed within the printhead are isolated from the ink or other fluid disposed within the channels.